If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.

1990 super coupe iwth some problems please help me if you can

I picked this car up its is a 5 speed it runs good after the tune up but there is a stumble if you press the pedal a little if you press it down 1/4 pedal or more it is fine and doesnt miss a beat. It pulls good boosts good, tps tested good, maf tested good, IAC is working. I fount the MAP sensor {see picture} shouldnt it be connected to some kind of vaccum line in the front where the nipple is??? there wasnt anything connected but electrical just wondering if anyone could help me on where to look I would appreciate it thanks.

It's not a MAP sensor, it's a BAP sensor and doesn't get a hose connected....just looks at barometric pressure. Sounds like you have a small vacuum leak. These leaks usually occur at one of the IC tube connections. If removing the tubes they must be resealed to hold vacuum and boost. You can buy a set of reusable Teflon gaskets or you can use a thin coating of Permatex high temp RTV like I do. Spraying IC tube connections with carb cleaner while motor is idling will usually identify where the leak is, but if that doesn't work a smoke test will show you where it's leaking.

I wish it was that easy, I took the pipes off myself and looked at a vaccum diagram everything is connected... Maybe a dead spot in the tps Im going to buy one if it isnt it I can always take it back thanks

tune up was coil, wires, plugs, tps, tps connector, MAF, MAF connector, IAC cleaning Throttle body gaskets redone, sprayed carb cleaner all over no rev ups also no jumping on the boost gauge which is vaccum. Also no check engine light is on I know it works as it came on when I turn key and I unplugged the IAC while running and it popped up of course the check gauges light is on but I think that because the gas gauge isnt working thanks for the help any other suggestions/tips would be appreciated Travis

Looks like the only thing the tune-up missed were the O2 sensors and the fule & air filters. Again, double check the plug wires. Do you know which spark plugs went in?

Just because the check engine light isn't on doesn't mean there might not be codes that will help. If you don't have a code reader/don't know the process to check, there are some shops/auto parts stores that will check for free.

> sprayed carb cleaner all over no rev ups also no jumping on the boost gauge which is vaccum.

The computer might be compensating faster than you can try that, and smoothing the engine out, masking your attempt to check for vacuum leaks, so be careful how much you rely on it to check that way.

Very true on the carb cleaner technique...... Air filter is new fuel filter is new sorry i forgot those also fuel pump and clutch... O2 sensor are my next guess but dont they only start to send signal when warm it does it worse when cold...can you tell me how to test these two o2 sensor with a voltmeter/ohm meter there a 3 wire which is new to me ive had either 1 or 4 thanks again Travis

I mentioned the O2 sensors in general as part of a tune-up, and not so much as a specific about your current issue, sorry. If they are old, I'd not bother testing and just swap them out. And rather than ohm them in the car, I'd pull codes to see if they are out of range, etc. If you take them out to check, them don't bother putting them back unless they are recent.

Can you explain again about the stumble...was it why you tried a tune up or did it start after?

Did a tune up because it would stumble badly and die at idle it just needed one.... The stumble only happens when you press the gas down a very little amount or under 1500rpms whiule driving it clears up and runs fine after that boosts fine as well just a hesitation when you take off really slow or like you would from a stop sign and your not racing if your racing it it does fine for some reason. Thanks for the help Travis

- Run the codes
- Replace the air filter
- Clean the new MAF wire...carefully
- Replace the IAC w/new
- You said the throttle body gaskets were redone...sounds like a good chance to induce a vacuum leak...might want to recheck that work - did anyone try to mistakenly adjust the idle screw?

I have no clue about the idle screw but I can see where someone could have messed with that I did the gaskets myself it did the same thing before and after I dont think they where bad but I changed them. How would I check the idle screw does anyone have a close up picture of one so I can count threads and see if mine is close thanks

Well went to replace the IAC there is a epoxy on the end of the IAC tword the firewall it was almost gone letting air leak into the IAC also I guess I ripped the old gasket putting it back after cleaning it. Needless to say it seems fixed now still a small stumble/pop when decelerating in gear now but it has a exhaust leak as well that is next to go get a exhaust that doesnt have holes in it.. HEY THANKS FELLAS for the help im sure I will be asking for more in the future if I decide to keep this car. Travis

Ok how many o2 sensors are on the car. Upstream only rite 2 of them? It is still bucking at low rpms nothing as bad as it was but still there going to try o2 sensors next. Will a exhaust leak cause this is sounds like it has a small one maybe a clogged cat? Any suggestions are welcome thanks.

Ok how many o2 sensors are on the car. Upstream only rite 2 of them? It is still bucking at low rpms nothing as bad as it was but still there going to try o2 sensors next. Will a exhaust leak cause this is sounds like it has a small one maybe a clogged cat? Any suggestions are welcome thanks.

hmm got a chance to run it today went 20 miles besides the poping from exhaust it runs fine still the studder at low rpms doesnt seem to do it in 345 gears mainly 1rst and second. Also something weird when coasting in neutral at speed it idles at 1500-1700 rpms I think someone messed with my idle screw or something that is weird it should be at 1000 or so at coast any info on this please help me thanks alot